Zechariah was the son of Jeroboam II. When Jeroboam II died, there was an interregnum of ten years, at the end of which he succeeded to the throne. He occupied it for only six months though, before being put to death by Shallum.
Shallum son of Jabesh conspired against Zechariah. He attacked him in front of the people, assassinated him and succeeded him as king. (2 Kings 15:10)
Shallum himself, reigned only for a month before he was put to death himself.
Then Menahem son of Gadi went from Tirzah up to Samaria. He attacked Shallum son of Jabesh in Samaria, assassinated him and succeeded him as king. (2 Kings 15:14)
With Zechariah the dynasty of Jehu came to an end. Menahem, who assassinated Shallum took over the throne.